A rotary machine such as a hard disk of a personal computer, an electric fan, a cutting device, and a power generation turbine is preferably designed with its imbalance as small as possible, and careful balancing is performed before shipment. However, since there is a limit to balancing of the rotary machine, an external force of a centrifugal force type is generated during an operation, and vibration occurs. Furthermore, there are also machines which inevitably generate large imbalance during its operation due to its performances as in the case of an electric washing machine and reciprocating machines which inevitably generate vibration to some degree due to its structure as in the case of an engine. In order to suppress vibration of these machines (hereinafter referred to as a vibrating body), an automatic balancer and a vibration compensator are proposed (see Patent Literature 1, for example).
FIG. 8 illustrates an example of an automatic balancer 1X. This automatic balancer 1X has a circumferential passage 30 having the same central axis as that of a rotary machine 32 (a centrifugal separator and the like, for example) and a balance modifier 31 movably arranged in the passage 30. Here, outline arrows indicate vibration direction Z of the rotary machine 32.
Subsequently, an operation of the automatic balancer 1X will be described. This automatic balancer 1X can suppress vibration of the rotary machine 32 by passive movement of the balance modifier 31 in the rotating passage 30 and relative standstill in the passage 30 when vibration occurs in the rotary machine 32. At this time, a position where the balance modifier 31 relatively stands still after it moves in the passage 30 is passively changed depending on an amplitude and a vibration frequency of the rotary machine 32.
On the other hand, the vibration compensator has a vibration detection sensor for detecting vibration of a machine such as a diesel engine and the like, a plurality of rotatable mass bodies arranged at appropriate positions in the machine, and a motor for changing a rotational speed or phase of each of the mass bodies. This vibration compensator can suppress vibration of the machine, by detecting vibration of the machine by the vibration detection sensor, by sending a control signal to each of the motors, and by changing the rotational speed or phase of each of the mass bodies.
However, the above-mentioned automatic balancer and the vibration compensator have some problems. First, the automatic balancer has a problem in which it amplifies an amplitude of the machine in a region with a vibration frequency (frequency) lower than a resonant frequency (or a resonance point).
Second, the automatic balancer has a problem in which self-excited vibration is generated in a region of a vibration frequency higher than the resonance point. That is, although the automatic balancer has a function of automatically suppressing vibration, the balance modifier and the like cannot be positively controlled, and thus vibration of the machine might be amplified in some cases.
Third, the vibration compensator requires a precise motor or a complicated control mechanism, and thus has a problem of a high cost.